The mathematical theory of knots and links grew out of two problems in classical physics [1]}. In 1833, while studying electromagnetism and mutual inductance, Gauss discovered a formula for the linking number of two closed curves in three-dimensional space [2]}. A few decades later, Lord Kelvin proposed his vortex model of the atom, in which different elements were imagined to arise from different patterns of knotted and linked vortex rings in the ether [3]}. Since then, knots and links have been studied in many other parts of physics [4]}, [5]}, [6]}, [7]}, including quantum field theory [8]}, [9]}, liquid crystals [10]}, plasmas [11]}, [12]}, Bose–Einstein condensates [13]}, [14]}, fluids [15]}, [16]}, superfluids [17]}, the biophysics of DNA and other polymers [18]}, [19]}, the mechanics of ropes and elastic rods  [20]}, [21]}, [22]}, [23]}, [24]}, classical field theory [25]}, knotted scroll waves in excitable media [26]}, [27]}, \(n\) -body choreographies in celestial mechanics [28]}, and electromagnetic waves and fields [29]}, [30]}, [31]}, [32]}, [33]}, [34]}, [35]}, [36]}.
